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High Definition Multimedia Interface (HDMI) Tutorial

What types of video are supported by HDMI?

HDMI has the capacity to support existing high-definition video formats (720p, 1080i, and even 1080p). It also has the flexibility to support enhanced definition formats such as 480p, as well as standard definition formats such as NTSC or PAL.

First we need to look at the types of video available and how they work, then look at whether they are compatible with HDMI.

The format of composite video is that of a picture only analog television signal before any sound signal is combined in and both signals are modulated onto an RF Carrier. Composite video is so named because it is usually a composite of three source signals, named Y, U, and V. Composite video uses an analog interface. Composite video uses one signal line to carry the entire set of signals.

S-video stands for separate video and may also be known as Y/C video. S-video uses two separate signals, color and brightness, to carry video data. It does not use the same cable to carry audio signals. S-video uses an analog interface and is video signal in analog. S-video is one type of component video. S-video is not like composite video, which carries the entire set of signals in one signal line. S-Video, as it is usually implemented, carries high-bandwidth 480i or 576i resolution video, for example, standard definition video. It doesn't carry audio on the same cable.

Component video consists of a video signal that has been split into at least two components. The types of analog component video include RGB analog component video, Y'PbPr analog component video, and S-video analog component video. The various RGB (Red, Green, Blue) analogue component video standards typically offer the best analogue video signals available in consumer electronics. RGB uses no compression and offers no real limit in color depth or resolution. Many televisions, especially in Europe and Japan, utilize RGB via the SCART connector. All arcade games, excepting early vector and black and white games, use RGB monitors. Analog RGB is slowly falling out of favor as computers obtain better clarity using Digital Video Interface, DVI, and home theater moves towards HDMI.

Digital Video Interface, or DVI, is actually a predecessor of HDMI. Digital Video Interface was made by the Digital Display Working Group (DDWG). The original design for DVI included conversion of analog signals by converting analog into a digital signal. This was done so that both analog and digital signal monitors could be accommodated by DVI. Data is transmitted by the use of transition minimized differential signaling (TMDS) protocol and provides a digital signal from a PC's graphics subsystem to the display unit. There are actually three types of DVI. There is DVI-A and this type of DVI is used for analog signals like VGA.

The second type of DVI is DVI-D. This type of DVI is used for digital signals, and this type of signal is the one that all home theater products use and that are intended for consumer home use. DVI-I is the third type of DIV. This type is a combination of DVI-A and DVI-D. There are two levels of performance are supported by DVI-I. These levels are single link and dual link. Currently all home electronics products are designed around the single link standard. A dual link cable, however, is 100 % compatible with a single link cable plus the dual link cable offers the benefit of adaptability in the future for any wide band width applications. DVD-I is a complete, fully digital video transport protocol that is supportive of all digital video formats including 480p, 480i, 540p, 720p,1080p, and 1080i.

HDMI technology uses a digital interface instead of an analog interface. With an analog interface the digital signal is converted to an imperfect analog signal, sent to the display unit, then the signal is converted back to digital so it can display the signal. When the cable is translated into analog, some of the signal's quality is lost. HDMI uses a digital interface which means that the signal starts out digital, stays digital through the transmission, and is received as a digital signal by the receiving display. Because there are no signal conversions this keeps the digital signal strong with no degradation.

Whether the video source is a PAL, NTSC or ATSC standard, HDMI will fully support it. The creators behind HDMI claims that it supports every video format in the consumer electronics industry. Due to the three TMDS channels each capable of 3.4Gbps bandwidth, HDMI supports video resolutions from 480p to 1080p and even higher, 1440p, and supports 48bit color resolutions in the RGB or YCbCr color space, with HDMI 1.3 adding support for xvYCC color space.

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